1. Field
The present invention relates to a lithographic apparatus.
2. Background
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In a lithographic apparatus, an article, such as a substrate, a mask or a fiducial to be placed in the radiation beam, is held by an article support member, for example, by a clamping electrode, vacuum suction or otherwise.
Typically, these articles are positioned in a single or multistage positioning procedure which includes alignment and/or height adjustment of the article. To this end, typically one or more contactless measurement systems are used, which measurement systems direct a radiation beam to the article for measurement purposes, e.g. by interferometric measurements or by the use of a grating image. Also, a projection system is typically used to transfer a patterned beam onto a target portion of the article, in particular, the substrate, for exposure purposes of the article. For all these radiation control systems, in particular, a positioning sensor system and/or a projection system, a desire arises for them to be very stably mounted in order for them to be able to provide measurements and/or exposed features with in the order of (sub-) nanometer accuracies. To this end, a conventional lithographic apparatus may provide a metrology frame used to hold and keep substantially in place equipment used to measure distances used to position the substrate and the like and/or to hold and keep substantially in place equipment used to transfer a pattern to the substrate. This metrology frame is a stabilized frame that is protected against vibrations from outside so that it creates a super stable environment or “silent world” wherein the lithographic process is carried out, in particular, the positioning of a substrate and transfer of a pattern onto a target portion of the substrate.
On the other hand, a lithographic apparatus has moving parts which increasingly move faster and faster (to increase throughput) and which put a burden on the stability of equipment in the lithographic apparatus, especially on the mounting of measurement and/or exposure equipment.